High shear process for dextrose production

ABSTRACT

Use of a high shear mechanical device in a process for production of starch hydrolysate by reacting starch with a hydrolytic agent makes possible a decrease in mass transfer limitations, thereby enhancing production of starch hydrolysate. A system for production of starch hydrolysate is also provided in which a reactor is configured to receive the output from a high shear device, which is configured to receive a starch and lysing reagent. The high shear device is configured to generate a fine dispersion or emulsion of lysing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Patent Application No. 60/946,608 filed Jun. 27, 2007, thedisclosure of which is hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

1. Technical Field

The present disclosure generally relates to the conversion of starch tosimpler carbohydrates, and more particularly to apparatus and methodsfor converting starch to dextrose. More specifically, the disclosurerelates to the reduction of mass transfer limitations for the hydrolysisof starch.

2. Background of the Invention

Starch can be hydrolyzed into simpler carbohydrates by acids, variousenzymes, or a combination of the two. There are many food productssynthesized by the hydrolysis of starch. The extent of conversion istypically quantified by dextrose equivalent (DE), which is roughly thefraction of the glycoside bonds in starch that have been broken.Maltodextrin is a lightly hydrolyzed (DE 10-20) starch product used as abland-tasting filler and thickener. Viscous solutions of various cornsyrups (DE 30-70) are used as sweeteners and thickeners in many kinds ofprocessed foods. Dextrose (DE 100), or commercial glucose (D-glucose),is prepared by the complete hydrolysis of starch. High fructose syrup isobtained by treating dextrose solutions with the enzyme glucoseisomerase, until a substantial fraction of the glucose has beenconverted to fructose.

In the United States, dextrose and high fructose corn syrup areparticularly important commercial food products. Dextrose is a whiteodorless tasteless granular or powdery complex carbohydrate having thechemical formula (C₆H₁₀O₅)_(x). Dextrose is the chief form ofcarbohydrate storage in plants and has additional applications inadhesives, laundering, pharmaceuticals, and medicine. High fructose cornsyrup is the principal sweetener used in sweetened beverages to lowerthe cost of production. A lower quantity of the high fructose corn syrupcan be used in recipes compared to glucose because fructose tastessweeter than glucose.

Historically, the starch wet-milling industry produced allstarch-derived syrups by acid hydrolysis. There are severaldisadvantages of the acid process that were corrected by replacing theacid process with a two-step process as disclosed in U.S. Pat. No.2,891,869. In the disclosure, the first step comprises solubilizing orliquefying refined raw starch to create a low DE syrup product.Liquefication is accomplished by limited hydrolysis at high temperatureusing either acid or thermostable endoamylases, such as those producedby Bacillus lichenformis. The second step comprises subjecting the lowDE syrups produced in the first step to more extensive hydrolysisreactions. The second step may also be known as saccharification. Thesecond step produces syrups consisting of low molecular weight sweetsugars using enzymes that are very specific with regard to the productsthey form. The overall procedure is thus referred to as an acid-enzymeor a double enzyme process depending on the mode of liquefaction.

The process of breaking a complex carbohydrate, such as starch orcellulose, into its monosaccharide components is also referred to assaccharification. U.S. Pat. No. 2,891,869 discloses the preparation ofcornstarch derived syrups using the acid-enzyme process. In thedisclosure, syrups of varying composition were prepared by altering thesaccharifying enzymes utilized. The patent discloses that fungalglucoamylase (GA) produces glucose as the sole product and that maltdiastase produces the disaccharide maltose as a major product. Syrupscontaining various proportions of these two sugars may be prepared bysaccharifying the substrate with a combination of glucoamylase and maltdiastase. Subsequent investigations have been concerned with thedevelopment of enzyme systems that increase the degree of starchsaccharification and thereby the yields of these products.

A number of procedures covering immobilized enzyme technology forcontinuous dextrose production from starch have been described. In thedisclosures regarding enzyme immobilization, immobilization of theenzyme glucoamylase has been the focus. Many methods of glucoamylaseimmobilization are available, for example, the methods described in U.S.Pat. Nos. 2,717,852; 3,519,538; 3,619,371; 3,627,638; 3,672,955;3,715,277; 2,783,101; and 3,950,222.

Accordingly, there is a need in the industry for improved methods ofproducing dextrose and other starch hydrolysates from starch, wherebyproduction rates are increased, improved reactant mixing, and lowerreactant requirements are commercially feasible.

SUMMARY OF THE INVENTION

A high shear system and process for accelerating production of high DEsyrups from starch is disclosed. The high shear process makes possible areduction in mass transfer limitations, thereby increasing the reactionrate and enabling a reduction in contact time, an increase in productyield and/or a reduction in enzyme/lysing agent usage. In accordancewith certain embodiments of the present invention, a process is providedthat makes possible an increase in the rate of a process for theproduction of low DE syrups from starch by providing for more optimalcontact of reactants than previously feasible. The process employs anexternal high shear mechanical device to provide mixing whichaccelerates reactant interaction.

These and other embodiments, features, and advantages will be apparentin the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the preferred embodiment of thepresent invention, reference will now be made to the accompanyingdrawings, wherein:

FIG. 1 is a cross-sectional diagram of a high shear device for theproduction of starch hydrolysate;

FIG. 2 is a process flow diagram according to an embodiment of thepresent disclosure for high shear production of starch hydrolysate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Overview

The present disclosure provides a system and method for the hydrolysisof starch comprising mixing carbohydrates and enzymes with a high sheardevice. The system and method employ a high shear mechanical device toprovide rapid contact and mixing of reactants in a controlledenvironment in the reactor/mixer device. The high shear device reducesthe mass transfer limitations on the reaction and thus increases theoverall reaction rate.

Chemical reactions involving liquids, gases, and solids rely on the lawsof kinetics that involve time, temperature, and pressure to define therate of reactions. Where it is desirable to react two or more rawmaterials of different phases (e.g. solid and liquid; liquid and gas;solid, liquid and gas), one of the limiting factors controlling the rateof reaction is the contact time of the reactants. In the case ofheterogeneously enzyme-catalyzed reactions, there may be an additionalrate limiting factor, namely, removing the reaction products from thesurface of the enzyme to enable the enzyme to catalyze furtherreactants.

In conventional reactors, contact time for the reactants and/or enzymeis often controlled by mixing which provides contact between two or morereactants involved in a chemical reaction. A reactor assembly thatcomprises a high shear device makes possible decreased mass transferlimitations and thereby allows the reaction to more closely approachkinetic limitations. When reaction rates are accelerated, residencetimes may be decreased, thereby increasing obtainable throughput.

High Shear Device

High shear devices (HSD) such as high shear mixers and high shear mills,are generally divided into classes based upon their ability to mixfluids. Mixing is the process of reducing the size of inhomogeneousspecies or particles within the fluid. One metric for the degree orthoroughness of mixing is the energy density per unit volume that themixing device generates to disrupt the fluid. The classes aredistinguished based on delivered energy density. There are three classesof industrial mixers having sufficient energy density to producemixtures or emulsions with particle or bubble sizes in the range of 0 to50 μm consistently.

Homogenization valve systems are typically classified as high-energydevices. Fluid to be processed is pumped under very high pressurethrough a narrow-gap valve into a lower pressure environment. Thepressure gradients across the valve and the resulting turbulence andcavitations act to break-up any particles in the fluid. These valvesystems are most commonly used in milk homogenization and may yieldaverage particle size range from about 0.01 μm to about 1 μm. At theother end of the spectrum are high shear mixer systems classified as lowenergy devices. These systems usually have paddles or fluid rotors thatturn at high speed in a reservoir of fluid to be processed, which inmany of the more common applications is a food product. These systemsare usually used when average particle, globule, or bubble, sizes ofgreater than 20 microns are acceptable in the processed fluid.

Between low energy—high shear mixers and homogenization valve systems,in terms of the mixing energy density delivered to the fluid, arecolloid mills, which are classified as intermediate energy devices. Thetypical colloid mill configuration includes a conical or disk rotor thatis separated from a complementary, liquid-cooled stator by a closelycontrolled rotor-stator gap, which may be in the range from about 0.025mm to 10.0 mm. Rotors may preferably be driven by an electric motorthrough a direct drive or belt mechanism. Many colloid mills, withproper adjustment, may achieve average particle, or bubble, sizes ofabout 0.01 μm to about 25 μm in the processed fluid. These capabilitiesrender colloid mills appropriate for a variety of applications includingcolloid and oil/water-based emulsion processing such as preparation ofcosmetics, mayonnaise, silicone/silver amalgam, and roofing-tarmixtures.

Referring now to FIG. 1, there is presented a schematic diagram of ahigh shear device 200. High shear device 200 comprises at least onerotor-stator combination. The rotor-stator combinations may also beknown as generators 220, 230, 240 or stages without limitation. The highshear device 200 comprises at least two generators, and most preferably,the high shear device comprises at least three generators.

The first generator 220 comprises rotor 222 and stator 227. The secondgenerator 230 comprises rotor 223, and stator 228; the third generatorcomprises rotor 224 and stator 229. For each generator 220, 230, 240 therotor is rotatably driven by input 250. The generators 220, 230, 240 areconfigured t0 rotate about axis 260, in rotational direction 265. Stator227 is fixably coupled to the high shear device wall 255.

The generators include gaps between the rotor and the stator. The firstgenerator 220 comprises a first gap 225; the second generator 230comprises a second gap 235; and the third generator 240 comprises athird gap 245. The gaps 225, 235, 245 are between about 0.025 mm (0.01in) and 10.0 mm (0.4 in) wide. Alternatively, the process comprisesutilization of a high shear device 200 wherein the gaps 225, 235, 245are between about 0.5 mm (0.02 in) and about 2.5 mm (0.1 in). In certaininstances, the gap is maintained at about 1.5 mm (0.06 in).Alternatively, the gaps 225, 235, 245 are different between generators220, 230, 240. In certain instances, the gap 225 for the first generator220 is greater than about the gap 235 for the second generator 230,which is greater than about the gap 245 for the third generator 240.

Additionally, the width of the gaps 225, 235, 245 may comprise a coarse,medium, fine, and super-fine characterization. Rotors 222, 223, and 224and stators 227, 228, and 229 may be toothed designs. Each generator maycomprise two or more sets of rotor-stator teeth, as known in the art.Rotors 222, 223, and 224 may comprise a number of rotor teethcircumferentially spaced about the circumference of each rotor. Stators227, 228, and 229 may comprise a number of stator teethcircumferentially spaced about the circumference of each stator. Inembodiments, the inner diameter of the rotor is about 11.8 cm. Inembodiments, the outer diameter of the stator is about 15.4 cm. Infurther embodiments, the rotor and stator may have an outer diameter ofabout 60 mm for the rotor, and about 64 mm for the stator.Alternatively, the rotor and stator may have alternate diameters inorder to alter the tip speed and shear pressures. In certainembodiments, each of three stages is operated with a super-finegenerator, comprising a gap of between about 0.025 mm and about 3 mm.When a feed stream 205 including solid particles is to be sent throughhigh shear device 200, the appropriate gap width is first selected foran appropriate reduction in particle size and increase in particlesurface area. In embodiments, this is beneficial for increasing catalystsurface area by shearing and dispersing the particles.

High shear device 200 is fed a reaction mixture comprising the feedstream 205. Feed stream 205 comprises an emulsion of the dispersiblephase and the continuous phase. Emulsion refers to a liquefied mixturethat contains two distinguishable substances (or phases) that will notreadily mix and dissolve together. Most emulsions have a continuousphase (or matrix), which holds therein discontinuous droplets, bubbles,and/or particles of the other phase or substance. Emulsions may behighly viscous, such as slurries or pastes, or may be foams, with tinygas bubbles suspended in a liquid. As used herein, the term “emulsion”encompasses continuous phases comprising gas bubbles, continuous phasescomprising particles (e.g., solid catalyst), continuous phasescomprising droplets, or globules, of a fluid that is insoluble in thecontinuous phase, and combinations thereof.

Feed stream 205 may include a particulate solid catalyst component. Feedstream 205 is pumped through the generators 220, 230, 240, such thatproduct dispersion 210 is formed. In each generator, the rotors 222,223, 224 rotate at high speed relative to the fixed stators 227, 228,229. The rotation of the rotors pumps fluid, such as the feed stream205, between the outer surface of the rotor 222 and the inner surface ofthe stator 227 creating a localized high shear condition. The gaps 225,235, 245 generate high shear forces that process the feed stream 205.The high shear forces between the rotor and stator functions to processthe feed stream 205 to create the product dispersion 210. Each generator220, 230, 240 of the high shear device 200 has interchangeablerotor-stator combinations for producing a narrow distribution of thedesired bubble size, if feedstream 205 comprises a gas, or globule size,if feedstream 205 comprises a liquid, in the product dispersion 210.

The product dispersion 210 of gas particles, globules, or bubbles, in aliquid comprises an emulsion. In embodiments, the product dispersion 210may comprise a dispersion of a previously immiscible or insoluble gas,liquid or solid into the continuous phase. The product dispersion 210has an average gas particle, globule or bubble, size less than about 1.5μm; preferably, the globules are sub-micron in diameter. In certaininstances, the average globule size is in the range from about 1.0 μm toabout 0.1 μm. Alternatively, the average globule size is less than about400 nm (0.4 μm) and most preferably less than about 100 nm (0.1 μm).

Tip speed is the velocity (n/sec) associated with the end of one or morerevolving elements that is transmitting energy to the reactants. Tipspeed, for a rotating element, is the circumferential distance traveledby the tip of the rotor per unit of time, and is generally defined bythe equation V (m/sec)=π·D·n, where V is the tip speed, D is thediameter of the rotor, in meters, and n is the rotational speed of therotor, in revolutions per second. Tip speed is thus a function of therotor diameter and the rotation rate. In certain embodiments, alteringthe diameter or the rotational rate may increase the shear rate in highshear device 200.

For colloid mills, typical tip speeds are in excess of 23 n/sec (4500ft/min) and may exceed 40 m/sec (7900 ft/min). For the purpose of thepresent disclosure the term ‘high shear’ refers to mechanicalrotor-stator devices, such as mills or mixers, that are capable of tipspeeds in excess of 5 m/sec (1000 ft/min) and require an externalmechanically driven power device to drive energy into the stream ofproducts to be reacted. A high shear device combines high tip speedswith a very small shear gap to produce significant friction on thematerial being processed. Accordingly, a local pressure in the range ofabout 1000 MPa (about 145,000 psi) to about 1050 MPa (152,300 psi) andelevated temperatures at the tip are produced during operation. Incertain embodiments, the local pressure is at least about 1034 MPa(about 150,000 psi). The local pressure further depends on the tipspeed, fluid viscosity, and the rotor-stator gap during operation.

An approximation of energy input into the fluid (kW/l/min) may be madeby measuring the motor energy (kW) and fluid output (1/min). Inembodiments, the energy expenditure of a high shear device is greaterthan 1000 W/m³. In embodiments, the energy expenditure is in the rangeof from about 3000 W/m³ to about 7500 W/m³. The high shear device 200combines high tip speeds with a very small shear gap to producesignificant shear on the material. The amount of shear is typicallydependent on the viscosity of the fluid. The shear rate generated in ahigh shear device 200 may be greater than 20,000 s⁻¹. In embodiments,the shear rate generated is in the range of from 20,000 s⁻¹ to 100,000s⁻¹.

The high shear device 200 produces an emulsion capable of remainingdispersed at atmospheric pressure for at least about 15 minutes. For thepurpose of this disclosure, an emulsion of gas particles, globules orbubbles, in the dispersed phase in product dispersion 210 that are lessthan 1.5 μm in diameter may comprise a micro-foam. Not to be limited bya specific theory, it is known in emulsion chemistry that sub-micronparticles, globules, or bubbles, dispersed in a liquid undergo movementprimarily through Brownian motion effects. The globules in the emulsionof product dispersion 210 created by the high shear device 200 may havegreater mobility through boundary layers of solid catalyst particles,thereby facilitating and accelerating the catalytic reaction throughenhanced transport of reactants.

The rotor is set to rotate at a speed commensurate with the diameter ofthe rotor and the desired tip speed as described hereinabove. Transportresistance is reduced by incorporation of high shear device 200 suchthat the velocity of the reaction is increased by at least about 5%.Alternatively, the high shear device 200 comprises a high shear colloidmill that serves as an accelerated rate reactor. The accelerated ratereactor comprises a single stage, dispersing chamber. The acceleratedrate reactor comprises a multiple stage inline disperser comprising atleast 2 stages.

Selection of the high shear device 200 is dependent on throughputrequirements and desired particle or bubble size in the outletdispersion 210. In certain instances, high shear device 200 comprises aDispax Reactor® of IKA® Works, Inc. Wilmington, N.C. and APV NorthAmerica, Inc. Wilmington, Mass. Model DR 2000/4, for example, comprisesa belt drive, 4M generator, PTFE sealing ring, inlet flange 1″ sanitaryclamp, outlet flange ¾″ sanitary clamp, 2HP power, output speed of 7900rpm, flow capacity (water) approximately 300 l/h to approximately 700l/h (depending on generator), a tip speed of from 9.4 m/s to about 41m/s (about 1850 ft/min to about 8070 ft/min). Several alternative modelsare available having various inlet/outlet connections, horsepower, tipspeeds, output rpm, and flow rate.

Without wishing to be limited to a particular theory, it is believedthat the level or degree of high shear mixing is sufficient to increaserates of mass transfer and may produce localized non-ideal conditionsthat enable reactions to occur that would not otherwise be expected tooccur based on Gibbs free energy predictions. Localized non-idealconditions are believed to occur within the high shear device resultingin increased temperatures and pressures with the most significantincrease believed to be in localized pressures. The increase inpressures and temperatures within the high shear device areinstantaneous and localized and quickly revert to bulk or average systemconditions once exiting the high shear device. In some cases, the highshear-mixing device induces cavitation of sufficient intensity todissociate one or more of the reactants into free radicals, which mayintensify a chemical reaction or allow a reaction to take place at lessstringent conditions than might otherwise be required. Cavitation mayalso increase rates of transport processes by producing local turbulenceand liquid microcirculation (acoustic streaming). An overview of theapplication of cavitation phenomenon in chemical/physical processingapplications is provided by Gogate et al., “Cavitation: A technology onthe horizon,” Current Science 91 (No. 1): 35-46 (2006). The highshear-mixing device of certain embodiments of the present system andmethods is operated under what are believed to be cavitation conditionseffective to dissociate the starch into free radicals; exposed to thehydrolytic agent for the formation of the dextrose products.

Description of High Shear Process and System for Conversion of Starch

High Shear System 100, hereinafter HSS 100, is suitable for theconversion of starch to low molecular weight sugars including dextroseand maltose. Although useful for the conversion of starch to othersugars, the following discussion will be made with respect to theconversion of starch to dextrose. In embodiments, HSS 100 is used in anenzyme-enzyme process. Typical enzyme-enzyme conversion processescomprise formation of starch slurry and contact of this slurry with astarch-liquefying enzyme, for instance, bacterial alpha-amylase. Thestarch slurry is heated to a temperature in the range of 80° C. to 90°C. to hydrolyze the starch partially. The partially hydrolyzed starch,which generally has a DE in the range of from about 10 to about 20, isthen treated with glucoamylase.

FIG. 2 is a flow diagram of a starch conversion process comprising ahigh shear device. As will be further discussed below, the disclosedprocess with high shear device enhances the conversion by improvingcontact of reaction species. FIG. 2 illustrates the basic components ofa representative high shear reaction system 100 including pump 5, highshear device 40, and reactor 10. In certain embodiments, the HSD 40 ispositioned between pump 5 and reactor 10.

Pump inlet stream 20 is in fluid communication with pump 5. Inembodiments, pump inlet stream 20 comprises an aqueous starch solution.Pump inlet stream may comprise a partially hydrolyzed starch solution.In further embodiments, the starch solution may be treated with acid orenzymes prior to pump inlet stream 20. In such embodiments, the aqueousstarch solution is liquefied and partially hydrolyzed by contact with aliquefying enzyme. In certain instances, pump inlet stream 20 comprisesa concentration of about 20% to about 40% starch, and preferably astarch concentration from about 35% to about 40% starch.

Pump 5 is configured to provide a controlled flow throughout high shearsystem 100. Pump inlet stream 20 comprising aqueous starch solutionenters pump 5. Pump 5 builds pressure of the pump inlet stream 20 andfeeds HSD 40 via pump outlet stream 12. Preferably, all contact parts ofpump 5 are stainless steel, for example, type 316 stainless steel. Inembodiments, pump 5 increases the pressure of pump inlet stream 20 togreater than about 203 kPa (2 atm). Alternatively, the pump 5 increasespressure to greater than about 2025 kPa (20 atm). The increased pressurecan be used to accelerate reactions. The limiting factor for pressure inHSS 100 is the pressure limitations of pump 5 and high shear device 40.Pump 5 may be any suitable pump, for example, a Roper Type 1 gear pump,Roper Pump Company (Commerce Georgia) or a Dayton Pressure Booster PumpModel 2P372E, Dayton Electric Co (Niles, Ill.).

Pump 5 is in fluid communication with HSD 40 via pressurized outletstream 12. Pressurized outlet stream 12 is in injected into HSD inletstream 13. In certain embodiments, pressurized outlet stream 12 and HSDinlet stream 13 are homologous. Alternatively, HSD inlet stream 13comprises pressurized outlet stream 12 that has undergone additionalprocessing. In certain embodiments, pressurized outlet stream is cooledor heated prior to injection into HSD inlet stream 13.

Dispersible reactant stream 22 is injected into HSD inlet stream 13.Dispersible reactant stream 22 may be injected in to HSD inlet stream 13for introduction to HSD 40. Alternatively, dispersible reactant stream22 is injected directly in to HSD 40. HSD inlet 13 may comprise a poorlymixed solution comprising pressurized outlet steam 12 and dispersiblereactant stream 22. Dispersible reactant stream 22 may be injectedsimultaneously with pressurized outlet stream 12 into HSD inlet stream13. In certain embodiments, pressurized outlet stream 12 and dispersiblereactant stream 22 are mixed prior to introduction to HSD inlet stream13.

Dispersible reactant stream 22 comprises a hydrolytic agent in solution.In embodiments, the hydrolytic solution comprises at least one acidand/or at least one hydrolytic enzyme. Alternatively, dispersiblereactant stream 22 comprises an acid/enzyme mixture. In embodiments,dispersible reactant stream 22 comprises an acid selected fromhydrochloric acid, sulfuric acid, oleum (or fuming sulfuric acid), andmixtures thereof. In some embodiments, acid stream 22 compriseshydrochloric acid. Further, the acid comprises a pH of between about pH1 and about pH 4. Dispersible reactant stream 22 may be heated to atemperature between about 70° C. and about 160° C. Further, dispersiblereactant stream 22 comprises a glucoamylase. In embodiments, dispersiblereactant stream 22 comprises a thermostable endo-amylase. Inembodiments, thermostable endo-amylase is produced from Bacilluslichenformis. The hydrolyzing enzyme may comprise a bacterialalpha-amylase enzyme. Alpha-amylase enzyme may be produced from manytypes of microorganisms, for example by certain Aspergillus speciesand/or Bacillus subtilis. Alpha-amylase is an enzyme capable of randomlysplitting the starch molecule into smaller chain units and may be usedin the enzyme-enzyme process as liquefying enzyme. Alpha-amylase doesnot selectively split off dextrose units and breaks only theα-1,4-glucosidic bond. Alpha-amylase is an endo-amylolytic enzymecapable of promoting almost random cleavage of α-1,4-glucosidic bondswithin the starch molecule. Alpha-amylase is elaborated by many types ofmicroorganisms such as members of the Bacillus subtilis species,Aspergillus niger and other species of the Aspergillus genus and maltedcereal grains. Alpha-amylase will not act upon the α-1,6-glucosidicbonds in the starch molecule to any significant degree. Glucoamylasewill act upon such bonds, but at a rate that is slower than is desiredin commercial applications.

HSD 40 is in fluid communication with HSD inlet stream 13, comprisingdispersible reactant stream 22, and pressurized outlet stream 12. HSD 40intimately mixes aqueous starch solution in pump outlet stream 12 withdispersible reactant stream 22 comprising acid and/or enzymes. HSD 40creates an emulsion of dispersible reactant stream 22 within high shearinlet stream 13. As discussed in detail above, the high shear device 40is a mechanical device that utilizes, for example, a stator rotor mixinghead with a fixed gap between the stator and rotor. HSD 40 combines hightip speeds with a very small shear gap to produce significant shear onthe material being processed. The amount of shear will be dependant onthe viscosity of the fluid. In high shear device 40, the aqueous starchsolution and acid-enzyme solutions are mixed to form an emulsioncomprising micro-globules and nano-globules of the acid/enzyme solutiondispersed in the aqueous starch solution. In certain instances, multiplehigh shear devices 40 are in fluid communication with HSD inlet stream13. Further, use of multiple high shear mixers aligned in series,perhaps with varying shear rates, is contemplated to enhance thereaction.

HSD 40 may form an emulsion of immiscible liquid reactants.Alternatively, HSD 40 increases the dispersion and mixing of miscibleliquid reactants in an emulsion. In certain instances HSD 40 a forms ahighly mixed liquid-liquid phase (e.g., a fine emulsion) which may alsoinclude the low DE hydrolysate product. In embodiments, the resultantemulsion comprises globules in the submicron size. In embodiments, theresultant dispersion has an average globule size less than about 1.5 μm.In embodiments, the mean globule size is less than from about 0.1 μm toabout 1.5 μm, preferably the mean globule size is less than about 400nm; more preferably, less than about 100 nm. In embodiments, the highshear mixing produces globules capable of remaining dispersed atatmospheric pressure for about 15 minutes or longer depending on theglobule size.

Without wishing to be limited to a particular theory to explain themechanical effects of high shear mixing in the high shear process, it isthought that when such emulsion is formed, the surface area availablefor the reaction between the two phases is significantly increased,leading to an increased rate of reaction. In embodiments, transportresistance is reduced by incorporation of external high shear device 40such that the velocity of the reaction is increased by a factor of fromabout 10 to about 100 times. The hydrolysis reaction may initiate oncethe emulsion has been formed. In this sense, hydrolysis could occur atany point in HSS 100 of FIG. 2 if conditions are suitable. Not to belimited by a specific method, it is known in emulsion chemistry thatsubmicron particles, bubbles, or globules dispersed in a liquid undergomovement primarily through Brownian motion effects.

HSD 40 is in fluid communication with reactor 10. Reactor 10 is any typeof reactor in which the liquefaction and/or hydrolysis of starch cancontinue. High shear device (HSD) outlet stream 18 comprises an emulsionof micron and/or submicron-sized globules, as discussed hereinabove. HSDoutlet stream 18 is fluidly connected to reactor inlet stream 19. HSDoutlet stream and reactor inlet stream 19 may be the same stream. Incertain instances, the HSD outlet stream 18 may be further processedbefore entering reactor inlet stream 19. Alternatively, HSD outletstream 18 may be recycled through the HSD 40 prior to introduction toreactor inlet stream 19. As discussed hereinabove, the liquefactionand/or hydrolysis of starch may begin in HSD 40, or HSD outlet stream 18prior to introduction to reactor 10.

In certain embodiments, HSD outlet stream 18 may be heated or cooledprior to introduction to reactor 10. In embodiments, the temperature forconversion of starch to low DE hydrolysate is less than about 160° C.The emulsion in HSD outlet stream 18 is maintained at a temperature offrom about 70° C. to about 160° C. and more preferably, from about 85°C. to about 105° C. In certain instances, the use of external heatexchangers for heating and/or cooling is within the scope of one or moreof the embodiments described and claimed herein. There are many suitableheat transfer devices known to those of skill in the art that may beused successfully without departing from the spirit of the describedembodiments. Such exchangers may preferably include, without limitation,shell-and-tube, plate, and coil heat exchangers, as will be known tothose of skill in the art. After processing by heat exchangers, HSDoutlet stream 18 is injected into reactor inlet stream 19 forintroduction to reactor 10.

Reactor inlet stream 19 is in fluid communication with reactor 10.Reactor 10 may be any reactor configured for the liquefaction and/orhydrolysis of starch. Reactor 10 may preferably be a continuous stirredtank reactor or a batch reactor, without limitation. Further, reactor 10may comprise a jacketed reactor. In certain embodiments, reactor 10 isconfigured as a holding tank for increased residence time, and/oragitation of reaction mixture. In embodiments, reactor 10 may primarilyserve to cool/hold reaction fluid, as much of the reaction occurs inexternal high shear device 40 and throughout HSS 100. Reaction heat maybe removed from reactor 10 via any method known to one skilled in theart. The use of external heating and/or cooling heat transfer devices isalso contemplated. Suitable locations for external heat transfer deviceswould be between the reactor 10 and the pump 5, between the pump 5 andthe high shear device 40, or between the high shear device 40 and thereactor 10. Any suitable heat exchanger known to those experienced inthe art may be used.

Reactor 10 is in fluid communication with a plurality of fluid conduits.Conduits may include supplemental reactant inlet 11, product stream 16,liquid stream 17, and recycle stream 21. Supplemental reactant inlet 11is configured for the introduction of further reactants to the reactor.In certain instances, additional acid or enzymes may be added to thereactor. Liquid stream 17 comprising, for example, water is removed fromthe reactor 10. Liquid stream 17 may comprise excess acid, or additionalliquid wastes for disposal. Recycle stream 21 is configured forrecycling portions of the reaction mixture through the HSS 100. Recyclestream 21 may fluidly couple the pump inlet stream 20 and the reactor 5.Further, recycle stream 21 may be in fluid communication with anyportion of HSS 100, in order to re-circulate or recycle, withoutlimitation, a portion of the reaction mixture. As understood by oneskilled in the art, the recirculation of a portion of the reactionmixture improves the product hydrolysate.

Product stream 16 drains reactor 10. Product stream 16 comprising low DEhydrolysate may be extracted from high shear system 100 via productstream 16. Upon removal from reactor 10, product stream 16 comprisingthe hydrolysate may be utilized in additional processes. Additionally,product stream 16 may be passed to further processing units downstreamof high shear system 100 for further processing as known to those ofskill in the art. In embodiments, the liquefied and partially hydrolyzedstarch comprise product stream 16. The partially hydrolyzed starchsolution comprises a low dextrose-equivalent (DE) product. The productstream 16 comprises DE value of less than about 20; preferably, the DEvalue is less than about 15 in product stream 16. In embodiments, theliquefied and partially hydrolyzed starch product stream 16 has adextrose equivalent (DE) value of at most about 20. Alternatively, thehydrolysate in the product stream 16 has a DE value of up to about 15.Conventional non-high shear acid-enzyme processes are disclosed, forexample, in U.S. Pat. Nos. 2,305,168; 2,531,999; 2,893,921; 3,012,944and 3,042,584. The contents of these patents are hereby incorporatedherein in their entirety for all purposes.

In embodiments, product stream 16 is in fluid communication with vessel50. Further, product stream 16 fluidly couples reactor 10 to vessel 50.Vessel 50 is configured for further hydrolysis. Vessel 50 comprisesenzyme inlet 14, de-branching enzyme inlet 15, and syrup product stream55. For example, low DE syrups in product stream 16 are subjected tofurther hydrolysis in vessel 50. In certain embodiments, vessel 50 isconfigured for additional enzyme mediated hydrolysis. Additional enzymesmay be added to the reaction mixture comprising product stream 16 viaenzyme inlet 14. Vessel 50 is preferably maintained at a pH betweenabout pH 3.0 and about pH 6.0. In FIG. 2, complete hydrolysis of low DEhydrolysate product stream 16 to low MW sugars is performed in vessel50. In certain embodiments, low MW sugars comprise high dextrose syrupswithdrawn from HSS 100 by syrup product stream 55.

Syrup product stream 55 may be produced by a number of hydrolysisreactions. In certain embodiments, HSS 100 produces high dextrose syrupsby saccharification of liquefied starches with glucoamylase, GA.Glucoamylases are dextrogenic exoamylases produced by various fungi(e.g., Aspergillus, Rhizopus). Most of the commercially available GApreparations are produced by Aspergillus sp. and are optimally activeover the pH range from about pH 4.0 to about pH 5.0. Further, the GApreparations are operationally stable at temperatures of about 60° C. Inembodiments, high dextrose syrups containing about 90% dextrose may beobtained by saccharifying product stream 16 with GA within a preferredpH range of about pH 4.3 to about pH 4.5. In certain embodiments, theinternal conditions of vessel 50 are maintained for extended periods,for example, about 3 to about 4 days.

The low DE liquefied starch hydrolysates in product stream 16 may betreated with soluble glucoamylase enzyme preparations to convert the lowdextrose equivalent starch hydrolysate in product stream 16 to dextroseor dextrose containing syrups. In embodiments, product stream 16 istreated with enzyme for the conversion of low DE hydrolysate to producesyrups comprising low molecular weight sweet sugars using enzymes thatare specific with regard to the products they form. In embodiments, thepH of vessel 50 is about pH 4.3 where glucoamylase is optimally activeis the typical pH employed by industry.

In certain instances, the operation of dextrose producing system, suchas HSS 100, has several additional requirements regarding saccharifyingenzymes. The enzymes must be capable of functioning at a high solidslevel. The enzymes must also be operationally stable at relatively hightemperatures, i.e., they must be thermostable. The thermostabilityrequirement is imposed for two reasons: (1) the risk of microbialcontamination is reduced, and (2) the rate of saccharification isincreased, which in turn enables increases the production capacity of aHSS 100 using existing equipment. Generally, HSS 100 requires that thesaccharifying enzymes be thermostable at temperatures above about 50° C.For example, glucoamylase derived from Aspergillus may be selected overthose produced by other genera, such as Rhizopus, because the former aremore thermostable.

Amylopectin is the principal component of certain starches. It is amixed linkage glucose homopolymer in which the glucosyl moieties arelinked by α-1,4 and α-1,6 glycosidic bonds. In embodiments, productstream 16 is treated with enzyme inlet 14 in vessel 50. Enzyme inlet 14comprises α-1,4 carbohydrase, in vessel 50, to produce a high DE sugarsyrup in syrup product stream 55. The α-1,4-carbohydrase which is mostcommonly used when a high dextrose syrup is desired, is a glucoamylase,such as that derived from Aspergillus niger, which will cleave α-1,4linkages. In embodiments, glucoamylase is introduced to vessel 50 byenzyme inlet 14.

Glucoamylase has been referred to in the art as glucamylase glucogenicenzyme, starch glucogenase, and gama-amylase. Glucoamylase is anexo-amylolytic enzyme that catalyzes the sequential hydrolysis ofglucose moieties from the non-reducing ends of starch or amylodextrinmolecules. Glucoamylase preparations are produced from certain fungistrains such as those of genus Aspergillus, for example, Aspergillusphoenicis, Aspergillus niger, Aspergillus awamori, and certain strainsfrom the Rhizopus species and certain Endomyces species. Glucoamylaseeffects the hydrolysis of starch proceeding from the non-reducing end ofthe starch molecule to split off single glucose units at the α-1,4 or atthe α-1,6 branch points. Commercially available glucoamylase enzymepreparations may comprise several enzymes in addition to theglucoamylase. For example, traces of proteinases, cellulases,alpha-amylases, and transglucosidases may be included. Whileglucoamylase is capable of hydrolyzing both, its activity for α-1,6 bondbranch points is considerably less than for α-1,4 bonds. Glucoamylasesare capable of cleaving both the α-1,4 and α-1,6 glycosidic bonds whichoccur in starch and in theory should be able to effect completeconversion. In practice, high yields are obtained when the starch issaccharified at a low solids level of less than about 10% (w/w).However, when the saccharifications are conducted at solids levels inthe range of about 30% (w/w) to about 40% (w/w), the dextrose content ofthe resultant syrup is substantially reduced due to the accumulation ofhigher degree of polymerization saccharide impurities. However, syrupsof lower dextrose content are acceptable due to the economic advantagesgained by conducting the saccharification at a higher starch solidslevel.

In embodiments, a starch debranching enzyme selected from glucoamylases,isoamylases, and pullulanases is added to vessel 50 via debranchingenzyme inlet 15. The diminished reaction rate of certain amylasesdiscussed hereinabove acting on the branch points impedes completesaccharification to dextrose using GA alone. The situation would beexpected to improve if the branch points were more efficientlyhydrolyzed. Debranching enzymes or α-1,6-glucosidases have recently beenused for their ability to break the α-1,6 linkages which are nothydrolyzed or broken by the action of α-amylase. See, for example, U.S.Pat. No. 4,734,364, which is hereby incorporated herein by reference,for all purposes. Although both of the enzymes possess some α-1,6debranching activity, the debranching enzyme is more potent thanglucoamylase and as a result the reaction time may be significantlyreduced by HSS 100.

The α-1,4 carbohydrase, which is most commonly used in the industry whena high dextrose syrup is desired, is a glucoamylase, such as thatderived from Aspergillus niger, which will cleave α-1,4 linkages. Inembodiments, debranching enzyme is added to at least 0.001 debranchingenzyme per gram dry substrate (units/gds) are used and preferably fromabout 0.10 units/gds to about 0.5 units/gds pullulanase. The amount ofglucoamylase is at least about 0.01 units/gds, and preferably about 0.15units/gds to about 0.3 units/gds of glucoamylase activity. In theseembodiments, the vessel 50 is kept at a pH ranging from about pH 4.0 toabout pH 5.3 and a temperature of about 55° C. to about 65° C.

The α-1,4 carbohydrase which is used when the desired syrup productstream 55 comprises a high maltose syrup is a maltogenic or maltoseproducing enzyme, such as sweet potato β-amylase. The amount of enzymeto be added is preferably the minimum amount required to convert theα-1,4 polysaccharides to maltose. Normally amounts of at least about 1units to about 4 units debranching enzyme per gram dry substrate(units/gds) are used. Larger amounts can be used but are lesseconomical. In these embodiments, vessel 50 is operated at a pH of aboutpH 4.5 to about pH 5.5 and a temperature of about 55° C. to about 60° C.

Amylo-1,6-glucosidase derived from Aerobacter aerogenes is added viadebranching enzyme inlet 15 to vessel 50 to effect conversion of low DEhydrolysate to dextrose. U.S. Pat. No. 3,897,305 describes a method forconverting starch to dextrose by saccharifying a low DE starch streamwith an enzyme system comprising glucoamylase and amylo-1,6-glucosidase.Implementing this enzyme system with HSS 100, starch may be hydrolyzedto a greater degree in vessel 50. The dextrose yield in syrup productstream 55 and rate of production are increased. In embodiments, theamount of the debranching enzyme in reactor 50 is at least 0.001 unitsand preferably will be from about 0.10 units/gds to about 0.5 units/gds.The amount of glucoamylase is at least about 0.01 units/gds andpreferably about 0.15 units/gds to about 0.3 units/gds of glucoamylaseactivity.

When the desired product is a high maltose syrup, the α-1,4 carbohydraseused comprises a maltogenic or maltose producing enzyme, such as sweetpotato β-amylase. The amount of enzyme to be added is preferably theminimum amount required to convert the α-1,4 polysaccharides to maltose.Normally amounts of at least about 1 units/gds to about 4 units/gds areused. It is feasible, though less economical, the use high quantities ofenzyme. In certain embodiments, saccharification in vessel 50 isconducted at a pH of from about 4.5 to about 5.5 and a temperature offrom about 55° C. to about 60° C.

In embodiments, vessel 50 may comprise α-amylase and immobilized GA. Thehydrolysis reaction in vessel 50 may be carried out according to U.S.Pat. No. 4,102,745 that describes a process for converting starch todextrose wherein a partially hydrolyzed starch solution, containing atleast 10 percent hydrolyzed starch, is contacted with an enzyme system.The starch solution is contacted with the enzyme solution underconditions whereby substantially complete conversion of the starch todextrose is achieved. The enzyme system comprises immobilizedglucoamylase and alpha-amylase selected from the group consisting ofsoluble alpha-amylase, immobilized alpha-amylase and mixtures thereof.Various procedures have been described for the immobilization ofglucoamylase, alpha-amylase, and amylolytic enzyme combinations. In theart methods of glucoamylase immobilization are presented, for example,in U.S. Pat. Nos. 3,783,101; 2,717,852; 3,519,538; 3,619,371; 3,627,638;3,672,955; 3,715,277; 2,783,101; and 3,950,222. Combining these methodswith HSS 100 feasibly increase the production of dextrose and starchhydrolysates. In embodiments, low DE syrup stream 16 is converted as,for example, described in U.S. Pat. No. 4,132,595 to high DE hydrolysateusing soluble glucoamylase and subsequently treated solely with animmobilized glucoamylase enzyme to in vessel 50 to produce a dextroseproduct stream 55

In embodiments, use of the disclosed process comprising reactant mixingvia external high shear device 40 provides a higher conversion of starchto dextrose and/or decreased volumes of lysing agent due to moreefficient mixing. The method comprises incorporating high shear device40 into an established process thereby enabling the increase inproduction, by greater throughput, compared to a process operatedwithout high shear device 40. Additional potential benefits of thismodified system include, but are not limited to, faster cycle times,reduced operating costs and/or reduced capital expense due to thepossibility of designing smaller reactors and/or operating the reactorat lower residence times. In embodiments, the process of the presentdisclosure provides for a residence time less than about ¾ the residencetime for conversion of starch to low DE hydrolysate in the absence ofexternal high shear mixing. In embodiments, the process of the presentdisclosure provides for a residence time of less than about ½ theresidence time (for the same conversion) when compared to conversion ofstarch to low DE hydrolysate in the absence of external high shearmixing.

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use ofthe term “optionally” with respect to any element of a claim is intendedto mean that the subject element is required, or alternatively, is notrequired. Both alternatives are intended to be within the scope of theclaim. Use of broader terms such as comprises, includes, having, etc.should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,and the like.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims that follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the preferred embodiments of the present invention.The discussion of a reference in the Description of Related Art is notan admission that it is prior art to the present invention, especiallyany reference that may have a publication date after the priority dateof this application. The disclosures of all patents, patentapplications, and publications cited herein are hereby incorporated byreference, to the extent they provide exemplary, procedural, or otherdetails supplementary to those set forth herein.

1. A method for producing starch hydrolysate, the method comprising:forming a dispersion comprising a hydrolytic solution and an aqueousstarch solution utilizing a high shear device, wherein the dispersioncomprises hydrolytic solution globules with a mean diameter of less thanabout 5 μm, and wherein the high shear device comprises at least onerotor and at least one stator; introducing the dispersion into a reactorfrom which a product comprising dextrose is removed, wherein theoperating temperature within the reactor is maintained at a temperatureof less than about 160° C.
 2. The method of claim 1 further comprisingpumping a reactant stream comprising aqueous starch solution to apressure of at least about 203 kPa to produce a pressurized stream. 3.The method of claim 1 wherein the hydrolytic solution globules in thedispersion have an average diameter of less than about 1.5 μm.
 4. Themethod of claim 1 wherein forming the dispersion comprises rotating theat least one rotor at a tip speed of at least 5 m/s.
 5. The method ofclaim 1 wherein forming the dispersion comprises rotating the at leastone rotor at a tip speed of at least about 20 m/s.
 6. The method ofclaim 4 wherein forming the dispersion comprises producing a localizedpressure of about 1000 MPa at the tip of the at least one rotor.
 7. Themethod of claim 1 wherein forming the dispersion comprises subjectingthe hydrolytic solution and aqueous starch solution to a shear rate ofgreater than about 20,000 s⁻¹.
 8. The method of claim 1 wherein formingthe dispersion comprises an energy expenditure of at least 1000 W/m³. 9.The method of claim 1 wherein the hydrolytic solution comprises acomponent selected from the group consisting of acids, hydrolyticenzymes, and combinations thereof.
 10. The method of claim 9 wherein theacids are selected from the group consisting of hydrochloric acid,sulfuric acid, oleum (fuming sulfuric acid), and combinations thereof.11. The method of claim 9 wherein the hydrolytic enzymes are selectedfrom the group consisting of alpha-amylases, beta-amylases,glucoamylases, isoamylases, glucosidases, carbohydrases, pullulanases,cellulases, and combinations thereof.
 12. The method of claim 11 whereinthe hydrolytic enzymes further comprise thermostable enzymes.
 13. Amethod for producing starch hydrolysate, the method comprising: forminga dispersion of hydrolytic solution globules in a solution comprisingaqueous starch by introducing the hydrolytic solution and the aqueousstarch solution into a high shear device and subjecting the mixture ofthe hydrolytic solution and the aqueous starch solution to a shear rateof at least 20,000 s⁻¹.
 14. The method of claim 13 wherein the highshear device comprises at least one rotor and at least one stator.
 15. Asystem for the production of starch hydrolysate, the system comprising;a high shear device comprising at least one rotor and at least onestator having a minimum clearance therebetween and configured to producea dispersion of hydrolytic solution globules in a solution comprisingaqueous starch, the dispersion having an average globule diameter ofless than about 5 μm; and a reactor fluidly connected to an outlet ofthe high shear device, wherein the reactor comprises apparatus such thatcontents of the reactor may be maintained at a temperature of less thanabout 160° C.
 16. The system of claim 15 wherein the high shear devicecomprises at least two rotors and at least two stators.
 17. The systemof claim 15 wherein the high shear device is adapted to rotate the atleast one rotor at a tip speed of at least 5 m/sec.
 18. The system ofclaim 15 wherein the high shear device is configured to produce alocalized pressure of at least about 1000 MPa at the tip of the rotorduring operation of the high shear device.
 19. The system of claim 15wherein the high shear device can produce a shear rate of greater thanabout 20,000 s⁻¹.
 20. The system of claim 15 wherein hydrolytic solutioncomprises a solution chosen from the group comprising acids, hydrolyticenzymes, or combinations thereof.
 21. The system of claim 20 wherein theacid is selected from the group comprising: hydrochloric acid, sulfuricacid, oleum (fuming sulfuric acid), and mixtures thereof.
 22. The systemof claim 20 wherein the at least one hydrolytic enzyme solution isselected from the group consisting of alpha-amylases, beta-amylases,glucoamylases, isoamylases, glucosidases, carbohydrases, pullulanases,cellulases, and combinations thereof.